Walk-behind vibratory compaction rollers are used to compact soil and asphalt in order to provide a firm foundation for structural building, to reduce future settlement of soil, or to compact asphalt for pathway, road, and parking lot construction. Such machines commonly are controlled by a single operator who follows behind the machine to direct the machine's travel direction and actuate its controls. Such machines may have one drum (single-drum) or two drums (dual-drum) acting as compaction surface(s). In order to enhance compaction, each drum is excited to vibrate by an exciter assembly associated with the drum. Commonly, a control arm extends rearwardly from the machine and provides the mechanical advantage to allow the operator to physically manipulate the direction of travel of the machine.
Vibratory rollers typically have either “center excitation” in which an exciter assembly is positioned between front and rear drums or “in-drum excitation” in which an exciter assembly is positioned within each drum that is excited. High vibration levels inducted in all vibratory compaction rollers can cause machine components to resonate at different frequencies. In some cases, the vibrating components can generate high sound levels on their own and/or through interaction with other components. The resulting noise is problematic because vibratory machines must meet strict sound limit regulations in various countries (particularly in the European Union). Measures therefore usually are taken to reduce noise generation. These measures typically include the use of design principals including resonance avoidance and the provision of dampening systems.
Noise reduction efforts are complicated by the basic design of vibratory compaction rollers. The drum or drums typically are mounted on a lower frame, and the engine, controls, and other components are mounted on an upper frame that is mounted on the lower frame via vibration isolating mechanisms such as shock mounts. In the case of a center-mounted exciter assembly, the exciter is mounted, or built into, the lower frame. Bearings and hydraulic drive motors are positioned between the drum supports and drums. These components between the lower frame and the drums require the provision of tolerance in the form of gaps between them to allow for relative movement therebetween while preventing binding. The large number of components leads to a large tolerance stack-up, even if many of the components are precision machined. Relative movement between any of these components can be excited with vibration, creating large amounts of sound.
Various techniques have been implemented to reduce noise generation due to operation of a vibratory compaction roller. Many of these techniques are reasonably effective, but most are relatively costly to implement and/or add cost, size, weight, and/or complexity to the machine. For example, one design uses a specialized motor to drive the drum to rotate. Another design uses specialized bearings. Both designs add considerable cost and complexity to the roller.
The need therefore has arisen to provide a technique for reducing sound generation during operation of a vibratory compaction roller that is effective, yet relatively simple and inexpensive when compared to previously-known techniques.